I., first of all, May God bless u guys as this is a very delicate baby and a special one too! I was reading your concerns and obviously you have a valid reason to be concerned because he is not eating what you think he should be. One thing my pediatrician always told me ,"They eat when they are hungry" just like that, end of story. And you know what, he was right, they are all striving and healthy. My daughter who is 12 months old, only had 4 oz of formula in a bottle feeding up until this last month, then she started taking 6 oz sometimes, not all the time. So he may not need more than what he is taking in and you don't want to force feed him because that too can make him sick, so be patient and let him dictate when he is hungry, this is a little frustrating because we want to know that they are doing what they are supposed to be but each child is very different, I know, I have 3. If he is happy then he has what he needs, so therefore there is no problem, always go with your motherly gut instinct, that is a still small voice in your head. I wish you much success and this too shall pass. God bless you, your son and your family!